Fuel Filter: A clogged fuel filter can restrict fuel flow to the engine, causing hesitation and bucking. Check the fuel filter and replace it if it is dirty or obstructed.
Spark Plugs: Worn or fouled spark plugs can cause misfires, leading to sputtering and bucking. Check the condition of the spark plugs and replace them if necessary.
Ignition Coils: Faulty ignition coils can also lead to misfires and poor acceleration. Check the ignition coils and replace any faulty ones.
Fuel Injectors: Dirty or clogged fuel injectors can disrupt the proper fuel flow to the cylinders. Clean or replace the fuel injectors as required.
Oxygen Sensor: A faulty oxygen sensor can cause the engine to run lean or rich, leading to performance issues. Check the oxygen sensor and replace it if it is faulty.
Mass Air Flow (MAF) Sensor: A faulty MAF sensor can provide incorrect information about air flow to the engine, resulting in poor fuel-air mixture and engine performance. Check the MAF sensor and replace it if needed.
Vacuum System: A vacuum leak can cause a lean fuel mixture and performance problems. Check the vacuum system for any leaks and repair them as required.
Throttle Body: A dirty throttle body can obstruct airflow and cause engine performance problems. Clean the throttle body and check its functionality, particularly its sensor's accuracy.
ECU: In rare cases, issues with the Engine Control Unit (ECU) can cause these symptoms. The ECU is responsible for controlling many aspects of the engine's operation, including fuel-air mixture, ignition timing, and emissions controls. If all other factors have been checked, it may be necessary to diagnose and potentially reprogram or replace the ECU.
Since you have mentioned that replacing the fuel pump did not resolve the issue, it is recommended that you systematically inspect and test each component mentioned above, starting with the most likely causes based on the symptoms. If the problem persists or if you are unable to identify the cause, it is best to consult with a professional mechanic or dealership experienced with your specific vehicle model. They can perform a more in-depth diagnosis and repair.
